"They can live in a wide range of temperatures from hot to cold. So living here in Chicago, this is a perfect climate for them," Maureen Leahy, curator of primates, said.

In the wild, the snow monkeys spend time in the volcanic hot springs. At Lincoln Park Zoo, they've got a manmade hot spring.

Snow monkeys develop red faces when they mature.

"That's really the signal from the males to the females that they're ready to breed," Ross.

The breeding season just ended and the males and females were kept apart so nothing is going to happen for a while. However, next September a new season starts and the macaques are going out on a limb to predict big changes here.

"The exhibit, being as large as it is, we should be able to have 20 to 25 troop members in the next five, ten, 15 years," Leahy said.